In the conventional blasting apparatuses, a pressured tank apparatus that supplies abrasive particles to a nozzle is constructed from a pressured tank as shown in FIG. 6, which is so called as a single direct-pressure type. In the drawing, the reference numeral 51 denotes such a pressured tank. On the pressured tank 51, there is provided a hopper 52. Between the pressured tank 51 and the hopper 52, there is provided a particle supply valve 56. The particle supply valve 56 is a pressure type shutoff valve which opens and closes automatically in accordance with the internal pressure of the pressured tank 51.
Further, connected to the top portion of the pressured tank 51 are an air supply pipe 55, which supplies air for the purpose of pressurizing the inside of the pressured tank 51, and an exhaust pipe 58 which exhausts the pressurized air within the pressured tank 51. For performing these functions, the air supply pipe 55 is provided with an air supply valve 54, and the exhaust pipe 58 is provided with an air release valve 57.
Connected to the bottom portion of the pressured tank 51 is a delivery pipe 60 for delivering compressed air and particles to a nozzle (not shown in FIG. 6). A particle supply valve 59 is provided in the delivery pipe 60. In the drawing, the reference numeral 53 denotes particles accumulated within the pressured tank 51.
Now, when the above described conventional blasting apparatus is to be used, first a prescribed amount of particles are supplied to the pressured tank 51 from the hopper 52. Then the exhaust valve 57 is closed and the air supply valve 55 is opened to allow pressurized air to pass into the pressured tank 51, whereby the pressure inside the pressured tank 51 is to be risen. As soon as the pressure inside the pressured tank 51 reaches a prescribed level, the particle supply valve 56 automatically closes, thus stopping the flow of particles 53 from the hopper 52 to the pressured tank 51 and, at the same time, preventing pressurized air from leaking into the hopper 52 from the pressured tank 51. Then when a blasting operation is to be carried out, the particle supply valve 59 is opened to allow particles to be delivered to the nozzle.
However, in the conventional blasting apparatuses, when all the particles 53 have been used up in the course of carrying out a blasting operation, the blasting operation must be suspended temporarily in order to refill the pressured tank 51 with the new particles 53. Namely, in the refilling operation, the air supply valve 54 must first be closed to stop the flow of pressurized air into the pressured tank 41 after the blasting operation has been suspended. At the same time, the exhaust valve 57 must be opened to exhaust pressurized air out of the pressured tank 51. Then, when the pressure inside the pressured tank 51 reaches a pressure that is roughly equal to the atmospheric pressure, the particle supply valve 56 automatically opens, which then allows particles 53 to flow into the pressured tank 51 from the hopper 52. Consequently, in the conventional blasting apparatuses, a great deal of time and many tedious operations are required for refilling the pressured tank 51, and therefore blasting operation must be suspended at each refilling operation. For this reason, there is a problem in that it is impossible to carry out a continuous blasting operation with such conventional blasting apparatuses.
In order to reduce the number of such suspensions which are caused by the refilling operations as much as possible, one attempt has been made to utilize a larger pressured tank that can accommodate a great deal of particles therein. In this way, it is possible to carry out a relatively longer blasting operation with one operation of particles.
However, even with the blasting apparatuses having such larger pressured tanks, it is still necessary to suspend blasting operations in order to refill the pressured tank, and therefore it is impossible to carry out continuous blasting operation. Further, such a larger pressured tank is more dangerous in comparison with a small pressured tank, and a manufacturing cost thereof is relatively high. Furthermore, there is a problem in that a place where such a blasting apparatus having a larger pressured tank is to be installed must be limited in view of its weight and a large amount of space which is required to install such a blasting apparatus.
In view of the problems in the conventional apparatuses described above, it is a first object of the present invention to provide a compact size pressured tank apparatus for use in a blasting apparatus which enables a continuous blasting operation to be carried out, as well as a method of switching the pressured tank apparatus. Namely, in the blasting apparatus, a plurality of small pressure tanks are employed, and a pressured tank from which particles are provided to a nozzle is selected from the plurality of pressured tanks and at the same time particles are supplied or refilled to another pressured tank which is not providing particles to the nozzle.
In the meantime, in the conventional blasting apparatuses, a particle supply valve is provided for performing or terminating the supply of particles which are to be fed to the nozzle.
As one example of such conventional particle supply valves, there is known a valve of the type as shown in FIG. 9.
The known valve has a valve housing 221 provided with an inlet port 222 into which particles flow, an outlet port 223 from which the particles flow out of the valve, and a control air inlet/outlet port 224 which allows control air to flow into or out of the valve.
Further, in the valve housing 221, there are provided two diaphrams 229, 230 which are made of flexible rubber and held by the valve housing 221 to partition the space inside the valve housing 221 into a first chamber 231 and a second chamber 232. In this construction, the inlet port 222 and the outlet port 223 are communicated with the first chamber 231, and the control air inlet/outlet port 224 is communicated with the second chamber 232.
Further, a metal pin 227 is passed through the middle portion of each of the two diaphrams 229, 230 and is fixed thereto. Fixed to the end of the metal pin 227 which lies in the first chamber 231 is a valve element 226, and fixed to the other end which lies in the second chamber 232 is a metal plate cap 228.
Now, when the valve is to stop supplying the nozzle (not shown in FIG. 9) with particles , control air is passed into the second chamber 232 through the control air inlet/outlet port 224 to pressurize the second chamber 232. This results in an increase in pressure inside the second chamber 232 which causes the flexible diaphram 230 to deform toward the first chamber 231, which in turn causes the valve element 226 to close off the valve seat 225, thereby closing off the inlet port 222.
Then, when the valve is to be opened to supply the nozzle with particles , control air is exhausted out of the second chamber 232 through the control air inlet/outlet port 224 in order to decrease the pressure inside the second chamber 232. As a result, the diaphram deforms toward the second chamber 232, thus causing the valve element 226 to be retracted from the shutoff position (i.e., it moves to the right side in FIG. 9). This then allows particles to flow into the first chamber 231 through the space between the valve seat 225 and the valve element 226. Thereafter, the particles flow out of the outlet port 223 and then supplied to the nozzle.
Further, the second chamber 232 is provided with an adjusting screw 233 and a handle 234 fixed to the screw 233 to allow the screw 233 to be rotated. The screw 233 is used to adjust the amount of retraction of the valve element 226 in order to adjust the amount of particles to be supplied to the nozzle. For example, when the amount of particles flowing through the valve is to be decreased, the screw 233 is rotated to increase its protruding length into the second chamber 232. In this case, the end of the metal cap 228 provided at the middle of the diaphram 229 that has been deformed into the second chamber 232 upon the supply of the particles is come into contact with the end of the screw 233, to restrict the retraction of the valve element 226. As a result, the amount of the space between the valve element 226 and the valve seat 225 is reduced, thereby achieving a reduction in the amount of supply of particles.
However, because the diaphrams 229, 230 of the conventional valves are made of rubber, they lose elasticity during the long-term use, and this results in a problem in that leakage of particles is liable to be caused. Namely, when control air is supplied to the second chamber 232 to deform the diaphram 230 toward the first chamber 231, it is not possible to obtain a required pressing force that pushes the valve element 226 onto the valve seat 225 if the diaphram 230 loses its elasticity. Consequently, the valve element 226 is pushed back due to the pressure of the particles, thus leading to the leakage thereof.
Furthermore, because the rubber diaphrams 229, 230 are flexible, it is not possible to guarantee an even movement of the metal pin 227. Namely, when the supply of particles is terminated, the metal pin 227 is normally moved to the left in the drawings. However, there is a case that the pin 227 moves slightly left-downward due to the weight of the valve element 226. In this case, since the valve element 226 which is fixed to the metal pin 227 does not properly engage with the valve seat 225, there is a case that a space is created between the valve element 226 and the valve seat 225, thus resulting in a problem in that particles and compressed air are leaked through the space.
Moreover, if the power to the blasting apparatus is accidentally shut off during a blasting operation and therefore the flow of control air to the second chamber 232 suddenly stops, there is another problem in that particles and compressed air are discharged from the outlet port 223. Namely, in the above condition, the valve element 226 is simply abutted onto the valve seat 225 by the restoring force of the diaphram 229, 230, so that they are easily retracted by the pressure of compressed air and particles, thus resulting in leakage of the compressed air and particles.
In view of the above described problems, it is a second object of the present invention to provide a leakproof particle supply valve for use in a blasting apparatus which uses a piston and a biasing means in the form of a regulating spring instead of a diaphram to avoid deterioration of flexibility characteristics.
Further, it is a third objection of the present invention to provide a particle supply valve equipped with a slide disc fixed to a valve rod to allow a seal to be maintained between a first chamber and a second chamber over a long period of time.
Furthermore, it is a fourth object of the present invention to provide a particle supply valve which can prevent leakage of pressurized air and particles from being caused, by holding the valve rod properly to close the valve seat at a predetermined position.
Moreover, it is a fifth object of the present invention to prevent discharge of pressurized air and particles which would be caused by an accident that the valve element is not retracted from the valve seat in a case where flowing and pressurizing of the control air accidentally stop during the blasting operation.
In the meantime, in blasting apparatuses, particle separators have been used for the purpose of recycling particles that have been used during a blasting process. Namely, in the blasting process, some of the particles are crushed into particle dust. However, in order to maintain a desired blasting performance, it is necessary for the particles to maintain their prescribed particle diameter. Therefore, it is necessary to provide a particle separator for removing such particle dust in order to reclaim the particles.
In the conventional apparatuses, a cyclone type particle separator is used as such particle separator. This particle separator separates reclaimable particles from particle dust and the like by utilizing a revolving air current which produces a centrifugal force. This utilizes the character that particle dust has a relatively small diameter rather than a prescribed particle and therefore the mass of the particle dust is smaller than that of the reclaimable particles.
In this connection, FIG. 14 is a longitudinal sectional side view of such a cyclone type particle separator, and FIG. 15 is a top plane view thereof.
In FIG. 14 the reference numeral 350 denotes a separating chamber. In the separating chamber 350, there is provided with an inlet port 351 which sucks a mixture of used particles and particle dust produced by a blasting process together with compressed air. Further, an exhaust port 354 is provided in a central portion of the separating chamber 350 in such a manner that is passes through the upper surface of the separating chamber 350.
Now, when the mixture of used particles and particle dust produced by a blasting process and compressed air are sucked into the inside of the separating chamber 350 through the inlet port 351, they form a revolving flow that valve seat in the direction indicated by the arrow 352 shown in FIG. 15. Then, due to the relatively large mass of each of such prescribed diameter reclaimable particles and the centrifugal force produced by such revolving flow, the reclaimable particles slowly move down toward the bottom of the separating chamber 350 as they flow in the vicinity of the inner circumferential side walls of the separating chamber 350. Upon reaching the bottom of the separating chamber 350, the reclaimable particles are collected in a hopper tank 355.
In this case, the unreclaimable particle dust flows more toward the center of the separating chamber 350 due to their relatively low mass. Consequently, such low-mass particle dust gets sucked out of the separating chamber 350 together with compressed air through the exhaust port 354, and then fed to a dust collector.
In FIGS. 14 and 15, a metal screen indicated by the numeral 353 is provided for preventing peeled coating or bits of paint which have a relatively large size and has been discharged during the blasting process with being mixed into the reclaimable particles. This is because there is a case that such peeled coating or bits of paint falls into the hopper tank 355 without being discharged from the discharge port.
However, because such conventional particle separators do not have any obstructive member inside the separating chamber for diffusing the mixture of reclaimable particles and particle dust, a mixture of large and small mass particles and particle dust is caused to flow in the vicinity of the inner circumferential side walls of the separating chamber 350 when the particle separator is in actual operation, thus rendering such centrifugal separation ineffective. Furthermore, it is not possible to achieve a sufficient centrifugal separation with such conventional separators because the mixture of reclaimable particles and particle dust either falls into the hopper tank 355 or is sucked out through the exhaust port 354 before the mixture has flowed even halfway around the inside of the separating chamber 350. For these reasons, such conventional particle separators do not perform an accurate separation of reclaimable particles and particle dust.
Furthermore, if relatively large material such as peeled coating which has been exhausted in the blasting process would enter into the separating chamber, the revolving air flow is disturbed. In the conventional apparatus, the centrifugal force required for the separation process is obtained by the stable revolving air flow, there is a problem in that such a disturbance of the revolving air flow deteriorates stable separation accuracy.
Accordingly, it is a sixth object of the present invention to provide a particle separating apparatus for use in a blasting apparatus which can achieve a highly accurate separation of particles by using a diffusion member instead of a centrifugal force, and thereby being able to have high accuracy of separation and excellence in stable particle separation accuracy.